1. Field of the Invention
The present invention relates to a photographing lens having a memory in which lens data peculiar to the photographing lens is stored.
2. Description of Related Art
A photographing lens (interchangeable lens) in a recent single lens reflex camera having an automatic focusing device is usually provided with a memory (e.g., ROM) in which lens data peculiar to the photographing lens is stored. The camera body is provided with a control means which communicates with the memory to read the lens data stored therein and performs predetermined arithmetic operations (exposure calculation and AF calculation) for calculating exposure factors (diaphragm value, shutter speed, etc.), the amount of defocus, and the amount of displacement of the focusing lens to be moved, etc., in accordance with the lens data which is based on predetermined algorithm and formula.
The lens data includes, for example, an apex value Avmin at an open aperture (open F-number), an apex value Avmax at a minimum aperture (maximum F-number), focal length data f, and object distance data, etc.
Part of the lens data varies in accordance with the photographing conditions. Namely, the lens data partly varies in accordance with the object distance in the case of a single focus lens, and varies in accordance with the focal length in the case of a zoom lens, respectively.
Accordingly, in the case of a single focus lens, the object distance is divided into a plurality of object distance zones, so that the lens data corresponding to the object distance zones are stored in predetermined memory areas of the ROM. In the case of a zoom lens, the focal length is divided into a plurality of focal length zones, so that the lens data corresponding to the focal length zones are stored in predetermined memory areas of the ROM. Namely, the lens data is stored for every photographing condition in a page-address system.
The object distance and the focal length are detected by an object distance detecting device and a focal length detecting device, respectively, so that the lens data stored in the pages corresponding to the data thus detected is outputted to the camera body as renewed lens data.
Table A shows a lens ROM in which lens data corresponding to six focal length zones is stored for every page (area), by way of example. As can be seen from Table A, each line represents stored data of each page. The numerical values (00, 10, 20, 30, 40, 50) represent the page addresses corresponding to the six focal length zones.
To store all lens data corresponding to the plurality of object distance zones or focal length zones for every page in the memory means, the latter must have a large memory (storing capacity).
TABLE A __________________________________________________________________________ LC Address 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 __________________________________________________________________________ 00 1A 94 00 65 83 02 11 84 51 6A 69 3C 01 30 95 03 10 1A 94 00 65 93 03 12 84 51 6A 69 34 0D 30 8D 03 20 1A 94 00 69 93 24 13 84 51 6A 69 30 19 30 7C 03 30 1A 94 00 79 A3 A5 14 84 51 6A 60 2C 21 30 6B 03 40 1A 94 00 9D A3 E6 15 84 51 6A 60 29 2D 30 62 03 50 1A 94 00 42 B3 E7 16 84 51 6A 60 25 35 30 5A 03 __________________________________________________________________________